Colorectal Cancer and the African-American Community

Timothy Woodward, M.D.; Consultant; Department of Gastroenterology, Mayo Clinic Jacksonville, FL

 

Background and Significance

Colorectal cancer is the second leading cause of cancer mortality in the United States.1 Between 1990 and 1997, the incidence trends for colorectal cancer have shown steep declines for whites.2 In contrast, there is suggested a leveling off and even a possible increase of the rates for blacks. 3, 4 The variations in colorectal cancer incidence and death rates by race/ethnicity, gender, age, and geographic area may be related to differences in risk factors, demographic characteristics, screening and medical practice.

The lifetime incidence of colorectal cancer among persons at average risk (age greater than or equal to 50; no predisposing factors) is relatively high at 6%.5 Colorectal cancer screening has a demonstrated impact upon life expectancy. Colorectal cancer decreases the life expectancy of U.S. residents age 50 to 54 years by 292 days and those 70 to 74 years by 70 days. Colorectal cancer is an excellent candidate for prevention through screening programs: 1) the disease is fatal when diagnosed late; 2) is curable when diagnosed at an early stage; and 3) the disease passes through a detectable asymptomatic stage. A recent study calculates that screening with fecal occult blood tests (FOB) extends expected lifetime of the two age groups by 51 and 12 days, respectively, whereas screening with sigmoidoscopy leads to increases of 86 and 21 days. Colonoscopic screening increases expected lifetime by 170 and 41 days, respectively. The extension of life through screening colonoscopy is two or three times longer than the extension achieved through flexible sigmoidoscopy or fecal occult blood tests, respectively.6

Colorectal Cancer Epidemiology in Minorities

Racial and ethnic disparities in incidence, mortality and survival rates and trends exist for this disease. Differences in colorectal cancer screening, early detection and treatment in minority communities are related to therapeutic outcomes. Age-adjusted incidence rates for men with colorectal cancer are highest for Alaskan native men, followed by Japanese, then African-American men. For women, the incidence is highest for Alaskan native women, followed by African-American, then Japanese women.7 Mortality rates in men are highest for African-Americans, followed by Alaskan natives, then Hawaiians. In women, mortality rates are highest for Alaskan natives, then African-Americans, then whites.

Additionally, investigators have reported a more proximal distribution of adenomas8 9 and cancer10 11 in African-Americans.

Colorectal cancer screening rates vary by race, income and education. Colorectal cancer screening practices of African-American and white patients at an urban university medical center were evaluated retrospectively in one study. It was demonstrated that physicians adhered poorly to colorectal cancer screening recommendations.12 Previous screening colonoscopy studies defining the background prevalence of adenomas in average-risk populations were largely white and, in some cases, almost exclusively men.13 14 15 A recent study evaluated screening colonoscopy in asymptomatic average-risk African-Americans aged 55 to 75 years.16 The results suggest that an asymptomatic African-American population have at least as high an overall prevalence of adenomas (41% in men and 29% in women) as in previous screening colonoscopy studies. As previously noted, right-sided lesions predominated.

Colorectal Cancer Screening: Available Methods and Current Limitations

Colorectal cancer screening practices by primary care physicians vary considerably from those recommended. A recent national survey revealed that many physicians offer screening to individuals in whom it is not appropriate.17 Of the respondents, 85% offered colorectal cancer screening. However, 50% continued screening indefinitely regardless of the patients age and 44% performed fecal occult blood test (FOBT) in individuals frequently (which produces many false positives) and without appropriate dietary advice. Only 52% would follow a positive FOBT with a colonoscopy.

The options for colorectal cancer screening are evolving. FOBTs have been used to screen colorectal cancer for close to three decades and continues to be the most frequently employed screening tool in North America.18 The familiar guaiac-impregnated card tests, e.g. Hemoccult (SmithKline Diagnostics, Palo Alto, CA), were developed in 1967.19 Guaiac is a compound extracted from a tree bark that becomes blue in the presence of adequate concentrations of peroxidase-like substances like heme and hydrogen peroxide. Guaiac tests are not specific for blood as they react with any peroxidase, e.g. red meat or plant foods rich in peroxidases. Vitamin C supplements can cause a false negative result with guaiac tests.20 All patients with positive results are recommended to undergo colonoscopy for identification and removal of adenomatous polyps and cancers. Several randomized controlled trials of serial Hemoccult screening demonstrated a mortality reduction of only 15-33% after 10 to 14 years.21 22 23 That is, despite aggressive FOBT screening over the length of these trials, patients screened still died from colorectal cancer at 67-85% the rate of those of the unscreened; colorectal cancer incidences were not affected.

Flexible sigmoidoscopy, compared with FOBT, can detect adenomas in the rectosigmoid colon. Three uncontrolled observation studies in which adenomas were removed found the incidence of cancer to be well below that expected for historical controls.24 25 26 However, a major limitation of flexible sigmoidoscopic evaluation is failure of the examination to inspect the proximal colon. The flexible sigmoidoscope is only 60 cm and thus only reaches less than half of the colorectal surface. Several studies have demonstrated that sigmoidoscopic screening has no effect on mortality from proximal colorectal cancers.27 28 Additionally, other factors such as inadequate depth of insertion29, and poor acceptance of this unsedated and uncomfortable procedure lead to concerns regarding flexible sigmoidoscopy as a single screening vehicle.

Colonoscopy has recently been evaluated as a primary screening test for average-risk patients. As outlined above, well-designed randomized, controlled trials and case-control studies strongly support the efficacy of FOBT and flexible sigmoidoscopy as a screening vehicle. However, both screening strategies are limited by poor rates of compliance as well as being demonstrably less sensitivity than colonoscopy.30 Two recent studies have shown that colonoscopy, as a primary screening test for average-risk patients, is feasible.31, 32 These studies demonstrate almost unequivocally that screening colonoscopy can effectively reduce colorectal cancer-related mortality and is, more than likely, more effective than fecal occult blood testing, flexible sigmoidoscopy or a combination of the two.

The important question is how much a colonoscopy screening program will cost. A screening model examined the cost-effectiveness of colonoscopy in screening for colorectal cancer.33 Compared with colonoscopy, screening with annual FOBTs costs less but saves fewer life-years. A screening strategy based on flexible sigmoidoscopy every 5 or 10 years is less cost-effective than the other two methods. The seeming cost advantage of FOBT and flexible sigmoidoscopy compared to colonoscopy is offset in part by the subsequent costs of medical care for missed cancers as well as the incurred additional costs of work-up of all positive findings. According to the authors of the aforementioned study, screening with colonoscopy reduces the lifetime cost of caring for colorectal cancer by more than 75%. A bill has recently been put before Congress requesting every 10 year screening colonoscopy for average risk patients as part of Medicare.

Though a national consensus may, in the near future, recommend colonoscopy as a screening modality, the practical issues are that there are not enough trained colonoscopists for the proposed screening schema. In addition, other, less invasive tools may help to target patients needing to undergo colonoscopy.

Multi-target DNA-based assay panel (MTAP) is a potential stool-screening test for colorectal cancer. MTAP is a test whereupon neoplasm-specific DNA alterations, exfoliated into stool from adenomas and tumors, are subsequently assayed through a multicomponent assay panel targeting point-mutations on K-ras, APC and p53 genes, as well as Bat-26 (a marker of microsatellite instability) and highly amplifiable or "long" DNA (L-DNA). A recent blinded pilot clinical investigation detected 20 (91%) of 22 colorectal cancers and (73%-82%) of adenomas >/= 1 cm.34 MTAP and other such DNA-targeted assays may represent a foreseeable noninvasive screening test for colorectal cancer.

Barriers to Screening

Low income and minority populations are of special importance in cancer control efforts for several reasons.35

  • Such populations are less likely to obtain cancer screening tests
  • More likely to be diagnosed with a cancer at a later stage
  • Income and education are found to be critical factors

Barriers to screening programs stem from a variety of issues and concerns. From the patient standpoint, active issues include socioeconomic concerns of potential lost wages and medical costs. Additionally, system barriers at times may present obstacles such as child/parent care concerns, transportation and location.

Racial and gender variation in colonoscopic procedures may arise, as well, from physician attitude. A study published in 1999 sought to understand how the technology available (the period measured was from 1986 to 1989) was utilized by physicians in Michigan with near-universal coverage available.36 The results showed that urban areas and communities with higher education levels had more sigmoidoscopic use. Among procedures used to examine the entire colon, isolated barium enema was used more frequently in African Americans, the elderly, and females. The newest technology at the time, colonoscopy, was used most frequently among white males.

In summary, there exist barriers to cancer screening; colonoscopy may contain inherent advantages as a screening vehicle but newer, less invasive technologies may be in the near future; and efforts need to be made to overcome disparities in utilization of screening vehicles.

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www.dcmsonline.org January, 2001/ Jacksonville Medicine